Constitutive innate immunity is a component of the pace-of-life syndrome in tropical birds

TLDR

The study examined how constitutive innate immunity, measured by whole‑blood bactericidal activity, relates to basal metabolic rate across 12 tropical bird species and within individual house wrens to explore links between life‑history pace and physiology. Researchers developed a novel in‑vitro assay that uses a single blood sample to quantify whole‑blood bactericidal activity, providing an integrated measure of constitutive innate immunity. Bactericidal activity varied widely among species and individuals, was not correlated with body mass or BMR overall, but species‑level activity was negatively correlated with mass‑adjusted BMR, indicating that slower‑pace species have stronger immunity, while within house wrens activity positively correlated with mass‑adjusted BMR, suggesting individual quality differences.

Abstract

We studied the relationship between one component of immune function and basal metabolic rate (BMR), an indicator of the ‘pace-of-life syndrome’, among 12 tropical bird species and among individuals of the tropical house wren ( Troglodytes aedon ), to gain insights into functional connections between life history and physiology. To assess constitutive innate immunity we introduced a new technique in the field of ecological and evolutionary immunology that quantifies the bactericidal activity of whole blood. This in vitro assay utilises a single blood sample to provide a functional, integrated measure of constitutive innate immunity. We found that the bactericidal activity of whole blood varied considerably among species and among individuals within a species. This variation was not correlated with body mass or whole-organism BMR. However, among species, bacteria killing activity was negatively correlated with mass-adjusted BMR, suggesting that species with a slower pace-of-life have evolved a more robust constitutive innate immune capability. Among individuals of a single species, the house wren, bacteria killing activity was positively correlated with mass-adjusted BMR, pointing to physiological differences in individual quality on which natural selection potentially could act.